IRVINE, Ca. — Golfers are urged to swing with care after scientists at the University of California, Irvine, proved that titanium-coated clubs can cause course-side vegetation to burst into flames.

Orange County Fire Authority Capt. Steve Concialdi said Wednesday that the results confirm a suspicion investigators have had for years: that titanium alloy clubs were the cause of at least two blazes on area golf courses, including one that burned 25 acres at Irvine’s Shady Canyon in 2010. A second fire, sparked at Arroyo Trabuco Golf Club in Mission Viejo, burned close to homes.

“The common denominator was each golfer used a titanium club, and hit the ball just out of bounds next to dry vegetation where the ground was extremely rocky,” he said.

Investigators who were “laughed at” when they first floated the golf club theory have been vindicated, according to Concialdi.

Scientists painstakingly re-created in the lab course the conditions on the days of the fires. Using high-speed cameras and electron microscopes, they found that if hit upon a rock, clubs containing titanium can produce sparks of up to 3,000 degrees that will burn for more than a second, said James Earthman, a chemical engineering and materials science professor and an author of the study.

“And that gives the spark plenty of time” to ignite nearby foliage, he said. “Titanium reacts violently with both oxygen and nitrogen in the air.”

In contrast, when standard stainless steel clubs were used, there was no reaction.

Most golf clubs have steel heads but many manufacturers also make ones with a titanium alloy component in the head. Such alloys are 40 percent lighter, which can make the club easier to swing, researchers said.

Concialdi said the Fire Authority is giving golfers using titanium clubs permission to break the rules and “improve their lie” — that is, to move their ball away from rocks and dry vegetation.